Read the SMS activation code automatically in Xamarin Forms instead of manually typing it by user

Question

I wrote a project with Xamarin Forms. When every user has signed up, I send him/her an activation Code to confirm it and the user has to insert it to enter the app. But I am

Answer 1

If you're already sure about your clients having a SIM card in their device, then you can create a token and authenticate backwards, sending an SMS containing your token to from clients' device to your number.

Pros:

• No blocked numbers: Sending messages from client is not blocked even if you're on their blacklist or they're blocking advertisements and unknown senders.
• No costs on your side for authentication.
• This works also in iOS which you can't read but can send messages.

Cons:

• Client may be using another number in another device. This can be overcome by creating easy-to-type tokens which expire fast enough not to attract brute force attacks.
• Client may not be able to send an SMS to your number due to several reasons including but not limited to not having enough account charge.